1. Field of the Invention
This invention involves the calculated performance improvements expected from a particularly new class of compounds, geminal-bis(difluoramino)-substituted heterocyclic nitramines, when formulated into explosives and propellants. However,the synthesis of certain examples of this class of compounds is difficult and nonintuitive. The certain examples that are particularly synthetically difficult are molecules that incorporate the geminal-bis(difluoramino)alkylene [C(NF.sub.2).sub.2 ] component and the nitramine component [N-NO.sub.2 ] in close proximity, especially when separated by only a methylene (CH.sub.2) link in order to maintain a low fuel-to-oxidizer component ratio and concomitantly high oxygen balance in the product molecule. This invention involves 5,5-bis(difluoramino)hexahydropyrimidine derivatives, related geminal-bis(difluoramino)alkylene derivatives, and novel precursors to these new derivatives, by the use of certain key intermediates which allow formation of this target structural subcomponent.
2. Description of the Related Art
The calculated performance improvements expected from geminal-bis(difluoramino)-substituted heterocyclic nitramines when formulated into explosives and propellants has been reported. [Miller, Materials Research Society Proceedings 1996, 418, 3] One example of a highly desirable structure, described by Miller, is a derivative of 5,5-bis(difluoramino)hexahydro-1,3-dinitropyrimidine which has the following formula: ##STR1##
wherein R.sup.2 is selected from the group consisting of hydrogen, alkyl, such as C.sub.1 -C.sub.2 alkyls, and substituted alkyl, such as protected hydroxymethyl and 1,2-ethanediyl. The highly desirable structure, given the acronym RNFX by Miller, exists when R.sup.2 is hydrogen.
Methodology for preparing a geminal-bis(difluoramino)-substituted nitrogenous heterocycle has been reported by Chapman et al. [Journal of Organic Chemistry 1998, 3, 15661], who describe the preparation of 3,3,7,7-tetrakis(difluoramino)octahydro-1,5-bis(4-nitrobenzenesulfonyl)-1, 5-diazocine; this intermediate has been converted to the corresponding nitramine, 3,3,7,7-tetrakis(difluoramino)octahydro-1,5-dinitro-1,5-diazocine, given the acronym HNFX [Chapman et al, Journal of Organic Chemistry, 1999, 64, 960]. However the preparation of cyclic derivatives of 2,2-bis(difluoramino)-N,N'-dinitro-1,3-propanediamine in which the nitramine components are linked with a single-carbon bridge, such as RNFX, has not been previously described.